The present invention relates to novel microorganisms, a method for obtaining the same, and a method for preparing erythritol by fermentation, using the same. More specifically, the present invention relates to Aureobasidium sp. SN-124A strain and its artificial mutants, Aureobasidium sp. SN-G42 and SN-.gamma.96, a method for obtaining such microorganisms, and a method for preparing erythritol by converting fermentable sugars to erythritol with said microorganisms.
It is well-known to prepare erythritol by fermentation, using microorganisms. The microorganisms so far known to be capable of producing erythritol include, for instance, those belonging to Debaryomyces sp. (U.S. Pat. No. 2,986.495), Pichia sp. (U. S. Pat. No. 2,986,495), Candida sp. (U. S. Pat. No. 3,756,917), Moniliella sp. (Antonie van Leeuwenhoek, 37(1971)107-118 and such), Aureobasidium sp. (Japanese Patent Laid-Open Publication No. 61-31091) and the like.
However, such known microorganisms have not still been used on an industrial scale due to their grave disadvantage that cannot practically be neglected.
More exactly, U.S. Pat. No. 2,986,495 discloses a method for preparing arabitol, glycerol and erythritol from monosaccharides with the use of Pichia sp. and Debaryomyces sp. microorganisms. According to this method, however, only a small amount of erythritol may be produced as the byproduct, which should be separated out and collected with considerable difficulty.
U. S. Pat. No. 3,756,917 teaches a method for the preparation of erythritol from hydrocarbons using Canadian sp. microorganisms. However, this method is of low productivity and so uneconomical due to the need that the substrate concentration be at most 20 %. Another disadvantage is that the product cannot be used for foods, since there is a likelihood that the starting hydrocarbons may remain in the product.
Antonie van Leeuwenhoek, 37, 107-118 (1971) and Applied Microbiology, 12, [3]240-246 (1964) describes a method for preparing erythritol from glucose with the use of Moniliella (Torula) sp. microorganisms. This method is characterized in that the ratio of conversion of glucose to erythritol is high and the substrate concentration of a culture media may be increased to a relatively high level, but has the disadvantage that a large amount of xanthane gum should be used for defoaming, since marked foaming occurs at the time of culture.
Japanese Patent Laid-Open Publication No. 61-31091 describes methods for preparing erythritol from monosaccharides with the use of Aureobasidium sp. microorganisms. These methods make it possible to prepare erythritol using a relatively high substrate concentration of a culture media and, hence, are valuable in its own way.
However, these methods are not always satisfactory owing to the disadvantages that the yield of erythritol are not only unsatisfactory relative to the amount of cells grown by microorganisms, but the optimum pH, temperature and the like are also narrow, and, even if such factors depart slightly from the optimum ranges, there is then a remarkable drop of the yield of erythritol.
As a result of screening performed in view of the aforesaid considerations and on the erythritol productivity of many microorganisms in order to obtain erythritol-producing microorganisms of high industrial significance, it has been found that novel microorganisms belong to Aureobasidium sp. and isolated from a soil within a starch plant in Okinawa Prefecture, Japan, show high erythritol productivity.